Photocatalytic CO reduction reaction on [TM(tpy)(ppy)] (TM = Re and Rh) species with a square pyramidal nitrogen-coordinated structure: a computational study.

The photocatalytic performance of d-block metal complexes with unsaturated coordination circumstances after one dative-bond cleavage has become an emerging domain. Especially, the photocatalytic CO reduction reaction (CORR) on the active center of d-block metals in tridentate/bidentate ligands with square pyramidal nitrogen-coordinated atoms has been reported. In this study, the photocatalytic CORR performance of six metals in [TM(tpy)(ppy)] as possible active candidates (TM = Fe, Co, Ru, Rh, Re, and Ir) for CO production was evaluated in detail using DFT computations. The theoretical data demonstrate that the screened-out [Re(tpy)(ppy)] exhibits superior photocatalytic CORR activity to other identical species due to the only downhill process for CO activation and the second one-electron photoreduction step as its lowest rate-limiting step of 38.41 kcal mol. Besides, [Rh(tpy)(ppy)] also possesses comparable CORR activity theoretically with the reported [Ir(tpy)(ppy)]. In addition, our calculations reveal that the electron-transfer processes along the CORR pathway on [TM(tpy)(ppy)] are mainly sourced from the tpy ligand. Therefore, our study paves the way for exploring the active species of metal complexes as photocatalysts for the CORR before executing the targeted experimental exploration on their precursor complexes to discover other qualified ones.